1. Field of the Invention
The present invention relates to a coating apparatus for coating a building board. More specifically, the present invention relates to a coating apparatus for sufficiently applying a coating material to the entire surface of a building board without forming an uncoated area, while conveying the building board.
2. Description of the Related Art
The surface of a building board usually has an uneven pattern as a design feature in order to improve the appearance of the building board. The board having the uneven pattern on the surface thereof is normally applied with a coating material in order to suppress the changes in size or other properties of the building board caused by absorption of water or to further improve the appearance of the building board.
As an apparatus for applying a coating material to the building board, there are a brushing apparatus for applying a coating material using a brush applied, a roll coater apparatus where a part of the surface of a rotating roll coater is dipped in a coating reservoir to apply the coating material thereof to the roll surface, and the coating material is moved by means of the roll, a spray apparatus for applying a coating material by spraying the coating material through a nozzle at the end of the spray, and a flow coater apparatus that allows a coating material to flow down from a side wall of a coating reservoir to form a film and applies the coating material by allowing a building board to pass through the film-like coating material.
The brushing apparatus is an apparatus in which the brush is dipped in the coating reservoir to apply the coating material to the brush, and then the coating material is applied to a building board by brushing the surface thereof using the brush. In this apparatus it is difficult to brush the surface of the building board with the brush evenly, and to apply the coating material to the building board while conveying the building board. Furthermore, application of the coating material is even more difficult with a large building board or a building board that has an uneven pattern on the surface thereof. Thus, there is a concern that some sections of the surface of the building board might not be applied with the coating material sufficiently, impinging on the properties or appearance of the building board. Moreover, bringing the brush into direct contact with the building board causes hard wear and deformation, in which case the brush needs to be replaced immediately.
In the roll coater apparatus, application of the coating material can be performed while conveying a building board to be coated, because the coating material applied to the roll is moved to a section on the building board that comes into contact with the roll. Also, when the surface of the building board is smooth, the coating material is moved and applied to the building board surface sufficiently. However, when the building board has an uneven pattern on the surface thereof, the roll cannot be brought into contact with the concave portions. Therefore, the coating material cannot be moved to the concave portions and consequently some sections on the surface of the building board cannot be applied with the coating material, impinging on the properties or appearance of the building board. Furthermore, when circulating the coating material, fragments or the like of the base material of the building board are most likely to be mixed into the coating material, in which case the fragments adhere to the roll, whereby some sections on the surface of the building board might not be applied with the coating material. In addition, the viscosity of the coating material to be used needs to be managed because the viscosity of the coating material affects the coating condition of the coating material.
In the spray apparatus, the coating material can be applied to a building board while conveying the building board, because the coating material is sprayed to the surface of the building board. Therefore, the coating material can be applied to even a building board that has an uneven pattern on the surface thereof. However, the amount of coating material varies between the concave portions and the convex portions. Therefore, the inclined surfaces of the concave and convex portions cannot be applied with the coating material sufficiently, and the coating material forms a pool in each concave portion, impinging the properties or appearance of the building board. Furthermore, when circulating the coating material, fragments or the like of the base material of the building board are most likely to be mixed into the coating material, in which case the fragments cause nozzle clogging, whereby some sections on the surface of the building board might not be applied with the coating material.
In the flow coater apparatus, the coating material can be applied evenly to a building board having a smooth surface. However, in the case of a building board having an uneven pattern on the surface thereof, a flow coater apparatus can apply the coating material to the inclined surfaces of the concave and convex portions that are provided on the conveyance traveling direction side, but cannot apply the coating material to the inclination surfaces of the concave and convex portions that are provided on the opposite side of the conveyance traveling direction, whereby some sections on the surface of the building board are not applied with the coating material, impinging on the properties or appearance of the building board. Furthermore, when circulating the coating material, bubbles are generated in the coating material and break the film-like coating material, whereby some sections on the surface of the building board might not be applied with the coating material. In addition, fragments or the like of the base material of the building board are most likely to be mixed into the coating material, in which case the fragments clog the side wall of the coating reservoir, whereby some sections on the surface of the building board might not be applied with the coating material.
In order to solve the problems described above, there is a method for applying a large quantity of coating material to a surface of a building board, but applying a large quantity of coating material generates bubbles in a coating liquid film or causes accumulation of the coating material in the concave portions on the surface of the building board. When the coating material accumulates in the concave portions of the surface, bubbles and coating irregularity are caused in a drying step, degrading the quality or appearance of the product. As a solution to these problems, Japanese Patent Application Publication No. H10-202158 discloses an apparatus that performs flow coating on a coated surface and thereafter blows air from behind the coated surface in its moving direction. However, although this apparatus eliminates the bubbles generated on the coating liquid film, the apparatus does not eliminate the risk of accumulation of the coating material in the concave portions on the surface of the building board.